The present invention relates to an optical fiber characteristic measuring method and apparatus. More particularly, the invention pertains to an optical fiber characteristic measuring method and apparatus for automatically and continuously measuring a number of parameters such as transmission loss and transmission bandwidth.
Optical fibers have transmission characteristics such as a transmission loss characteristic, scattering characteristic and transmission bandwidth characteristic. Of these characteristics, the transmission loss characteristic and the transmission bandwidth characteristic are most important.
Heretofore, the transmission loss characteristic has been measured according to a transmission method in which the amount of attenuation of light propagating in an optical fiber under measurement is measured, or according to a back scattering method of measuring Rayleigh scattered light and Fresnel reflection light in an optical fiber under measurement. The transmission bandwidth characteristic is usually measured using the transmission method. In any one of the above-described methods, it is essential to couple the optical fiber to be measured to optical fibers provided on the side of a measuring device (see "Optical Fiber Cable", Hideo Fukutomi, Ohm Co., July 10, 1983, pp. 255-302). Accordingly, the degree of coupling of an optical fiber to be measured to optical fibers provided on the side of the measuring device greatly affects the accuracy and efficiency in measurement of the optical fiber characteristic measuring apparatus.
FIG. 1 is a diagram outlining the arrangement of a conventional optical fiber characteristic measuring apparatus operating in accordance with the transmission method. As shown in FIG. 1, aligning stands 1A and 2A, 1B and 2B and 1C and 2C are adapted to hold two end portions 3 and 4 of an optical fiber under measurement and to cause the end faces of the two end portions 3 and 4 to abut against the end faces of optical fibers 5A and 6A, 5B and 6B, and 5C and 6C provided on the side of measuring devices, and to align the two end portions 3 and 4 with the optical fibers 5A and 6A, 5B and 6B, and 5C and 6C. First end portions of the optical fibers 5A, 5B and 5C, and 6A, 6B and 6C are held by holders 7A, 7B and 7C, and 8A, 8B and 8C, respectively. The other end portions of the optical fibers 5A, 5B and 5C are connected to optical detectors 7A', 7B' and 7C', respectively. The other end portions of the optical fibers 6A, 6B and 6C are connected to light sources 8A', 8B' and 8C', respectively. The above-described components are, in general, installed on the surface of a table (not shown) as an integral unit. In FIG. 1, reference numeral 9 designates a bobbin on which the optical fiber to be measured is wound.
The operation of the measuring apparatus thus constructed will be described.
First, two end portions of an optical fiber to be measured are set on the aligning stands 1A and 2A after being suitably treated (the covers removed and the fibers cut). Then, the end faces of the two end portions 3 and 4 of the optical fiber under measurement are abutted against the end faces of the optical fibers 5A and 6A held by the holders 7A and 8A, respectively, and the two end portions 3 and 4 are aligned with the optical fibers 5A and 6A, respectively. This adjustment is carried out by aligning mechanisms (not shown) provided on the aligning stands 1A and 2A. Each aligning mechanism can finely displace the respective end portion of the optical fiber in the axial direction thereof, i.e., in Z direction, and in two other directions perpendicular to each other and to the axial direction of the optical fiber, i.e., in X and Y directions. The adjustment can be achieved with a three-direction (X, Y, Z) micromotion stand, or it can be carried automatically.
After the adjustment has been accomplished, light from the light source 8A' is applied to the optical fiber under measurement, and the optical detector 7A' measures the light propagating through the optical fiber. Thus, one measurement parameter, such as transmission loss, has been measured at the station I. Next, the bobbin 9 is manually shifted to the next station, and the operator similarly measures the other characteristics of the optical fibers at stations II and III in succession.
In the measurement of the characteristics of an optical fiber with such an optical fiber characteristic measuring apparatus, the period of time required for manual operations such as preparations for coupling two ends of an optical fiber to be measured to the ends of optical fibers provided on the side of a measuring device (treating the end faces of the optical fiber to be measured, setting the end portions of the optical fiber on the aligning stands, coupling the two ends of the optical fiber to be measured with the ends of the optical fibers provided on the side of the measuring device, and removing the optical fiber after measurement) is substantially equal to the period of time required for making actual measurements with the device and processing the measurement data. Accordingly, the number of measurement parameters which can be handled by one operator simultaneously is only one; that is, the conventional measuring apparatus is considerably low in its efficiency of measurement.